The present invention relates to a resistor and a method of manufacturing the same.
There has been a growing demand more than ever in recent years for miniaturization of electronic components used for circuit boards, in order to increase a density of mounting, as reduction in size of electronic devices continues. A demand has been rising also for resistors having smaller size and higher accuracy in tolerance of resistance values, in order to reduce mounting areas on mount boards.
Previously known resistors of such kind include one that is disclosed in Japanese Patent Laid-open Publication, Number H04-102302.
A resistor of the prior art and a method of manufacturing the same will be described hereinafter by referring to accompanying figures.
FIG. 50 is a sectional view depicting a resistor of the prior art.
In the figure, a reference numeral 1 represents an insulating substrate, and a reference numeral 2 represents first upper surface electrode layers provided on an upper surface at both right and left ends of the insulating substrate 1. A reference numeral 3 represents a resistance layer provided in a manner that portions of which overlap with the first upper surface electrode layers 2. A reference numeral 4 represents a first protective layer provided in a manner to cover the resistance layer 3 entirely. A reference numeral 5 represents a trimmed slit provided in the resistance layer 3 and the first protective layer 4 for correcting a resistance value. A reference numeral 6 represents a second protective layer provided over an outer surface of the first protective layer 4. A reference numeral 7 represents second upper surface electrode layers provided on upper surfaces of the first upper surface electrode layers 2 in a manner to spread over a full width of the insulating substrate 1. A reference numeral 8 represents side surface electrode layers provided on side surfaces of the insulating substrate 1. Reference numerals 9 and 10 respectively represent nickel-plated layers and solder-plated layers provided over surfaces of the second upper surface electrode layers 7 and the side surface electrode layers 8.
A method of manufacturing the resistor of the prior art constructed as above will be described hereinafter by referring to accompanying figures.
FIG. 51 represents procedural views depicting a method of manufacturing the prior art resistor.
Firstly, first upper surface electrode layers 2 are print-formed on both right and left ends of an upper surface of an insulating substrate 1, as shown in FIG. 51(a).
Secondly, a resistance layer 3 is print-formed on the upper surface of the insulating substrate 1 in a manner that portions of which overlap with the first upper surface electrode layers 2, as shown in FIG. 51(b).
Then, a first protective layer 4 is print-formed to cover the resistance layer 3 entirely, followed by providing a trimmed slit 5 in the resistance layer 3 and the first protective layer 4 with a laser or the like, as shown in FIG. 51(c), in order to make a resistance value of the resistance layer 3 to fall within a predetermined range of resistance value.
A second protective layer 6 is then print-formed on an upper surface of the first protective layer 4 as shown in FIG. 51(d).
Second upper surface electrode layers 7 are then print-formed on upper surfaces of the first upper surface electrode layers 2 in a manner that they spread over an entire width of the insulating substrate 1 as shown in FIG. 51(e).
Side surface electrode layers 8 are coat-formed on side surfaces at both right and left ends of the first upper surface electrode layers 2 and the insulating substrate 1, in a manner to make an electrical continuity with the first and the second upper surface electrode layers 2 and 7, as shown in FIG. 51(f).
The resistor of the prior art is completed finally, when nickel-plated layers 9 and solder-plated layers 10 are formed by providing solder-plating after nickel-plating over surfaces of the second upper surface electrode layers 7 and the side surface electrode layers 8.
However, as shown in a sectional view of FIG. 52(a) depicting the resistor of the prior art in a mounted position, the resistor having the above structure of the prior art and produced by the manufacturing method described above has a fillet-mounting structure, in which it is soldered with both the side surface electrode layers (not shown in the figure) and the lower surface electrode layers (not shown in the figure), when it is soldered on a mount board. The resistor thus requires areas 13 for soldering the side surfaces in addition to an area 12 for the resistor component, and therefore a mounting area 14 combining them altogether, as shown in a plan view of FIG. 52(b) depicting of the resistor of the prior art. Furthermore, a proportion occupied by the soldering area with respect to the mounting area increases, if external dimensions of the component are reduced in order to increase a density of mounting. Consequently, the resistor has a problem that a limitation arises in the improvement of mounting density in order to reduce size of electronic devices.
The present invention is intended to solve the above-described problem of the prior art, and it aims at providing a resistor, as well as a method of manufacturing, that can reduce a soldering area occupying in the mounting area, when it is mounted on the mount board.
In order to solve the foregoing problem, a resistor of the present invention comprises: a substrate; a pair of first upper surface electrode layers provided on side portions of an upper surface toward a portion of respective side surfaces of the substrate; a pair of second upper surface electrode layers provided in a manner to make electrical connections with the first upper surface electrode layers; a resistance layer provided in a manner to make electrical connections with the second upper surface electrode layers; and a protective layer provided to cover at least an upper surface of the resistance layer.
In the above-described resistor, electrodes on side surfaces of the resistor have small surface areas, since the resistor is provided with the pair of first upper surface electrode layers on side portions of the upper surface toward portions of side surfaces of the substrate. Because the resistor is soldered with the small areas of the electrodes on side surfaces, it can reduce an area required to form fillets for soldering, if it is soldered on a mount board. Accordingly, the resistor is able to reduce a mount area, including soldering portions, on the mount board.